A fing wot I lernt

[Sandman_bm]

Having got the trike ready to add all the electrickery,, fitted the PAS magnet ring and sensor for short cable run on the left side of the mid drive BB, powered up and nothing....... peddle backwards and the motor spun happily in the right direction., using my last braincell I deduced the magnet disc was facing the right way so all was left was the sensor, rotated that 180 degrees in its mounting and all was well, seem there is a directional sensitivity on these beasties, are they just more than one Hall Effect device because I dont see how a magnet passing over it from left to right or right to left can cause that unles its a software and flux variation with timing can make the
difference.
anyone got an explanation I can understand ?
regards
John

 

[Deleted member 4366]

Rather than swap the sensor round, which can be difficult on some systems, you can flip the magnet disc.

Hall sensors work on magnetic flux. The flux is directional, so a north facing magnet passing from right to left is seen as the same as a south facing pole coming from left to right. The hall sensor only switches on when the flux passes in the right direction.

Imagine a coil of wire connected to a voltmeter. If you pass a magnet from right to left, it makes a positive voltage, and fromleft to right it makes a negative one. Now put a diode between the coil and the voltmeter and you'll only get voltage one way.

 

[Sandman_bm]

Thank you for the reply which explained everything so clearly d8veh, I did flip the magnet disc to try it , and that resulted in no hint of life from the motor but it now works with reversed sensor.
regards
John